Cell culture has generated considerable interest in recent years due to the revolution in genetic engineering and biotechnology. Cells are cultured to make for example proteins, receptors, vaccines, and antibodies for therapy, research, and for diagnostics.
It has long been recognized that perfusion culture offers relatively good economics for cell cultures. In this operation, cells are retained in the bioreactor, and the product is continuously removed along with toxic metabolic byproducts. Feed, containing nutrients, is added continually to the bioreactor. Perfusion culture operation is capable of achieving high cell densities and more importantly, the cells can be maintained in a highly productive state for weeks. This achieves much higher yields and reduces the size of the bioreactor necessary. It is also a useful technique for cultivating primary or other slow growing cells.
Perfusion operations have been greatly developed during recent years. U.S. Pat. No. 6,544,424 discloses a perfusion system where a reciprocating diaphragm pump during the outward stroke pulls culture liquid from the bioreactor through a hollow fiber filter and during the inward stroke pushes the liquid back through the filter to the bioreactor. During the outward stroke, permeate is generated and during the inward stroke, the filter is backflushed to reduce the clogging by cells. Further developments of this technology are described in WO 2012/026978, relating to incorporation of the bioreactor and the perfusion unit into a single apparatus and in US 2011/0111486, where the flow to and from the perfusion unit is also used to provide additional agitation in the bioreactor. However, the filtration efficiency of these systems is not optimal, and they are still sensitive to clogging and fouling of the membranes.
Accordingly there is a need for improved designs of perfusion systems, allowing better control of the filtration.